1. Field of Invention
This invention relates in general to magnetic disk storage devices and, in particular, to an improved cooling and filtration system for the head disk assembly (HDA) of magnetic disk storage devices.
2. Description of the Prior Art
The prior art discloses various magnetic disk storage devices and various arrangements for cooling such devices. Cooling arrangements for disk files are needed to both limit the temperature to safe operating limits and to stabilize the temperature to which the disks, magnetic transducers, and various mechanical components are subjected. It is well known that considerable heat is produced by the rotating disks, and the amount of heat that is generated is related to the size of the disk and the rotational speed of the disk stack.
The ability to increase storage capacity on the disk surface is directly related to stabilizing the temperature in the environment of the head disks since a change in temperature does affect the positional relationship of the various components of the recording system. It is also known that considerable improvement in capacity can be obtained by decreasing the spacing between the magnetic transducer and the disk surface.
As the head to disk spacing is decreased, it becomes readily apparent that the prior art cooling arrangements, which were normally of the open loop type cooling systems, require some type of filter in order to insure that particles in the air being used to stabilize the temperature are smaller than the head to disk spacing.
While the provision of the filter in an open loop system avoids the problems of head crashes due to particles in the cooling air, it increases the impedance of the open loop air path and imposes a requirement to periodically check and replace the filter. It soon became readily apparent that with an open loop system cooling arrangement having a filter, any required increase in the volume of cooling air which might have been prompted by the desire to add additional disks, increase the disk size, or operating speed, materially shortens the life of the filter. Similarly, any decrease in the head to disk spacing required a finer filter and an increase in impedance in the air path, and also a shorter filter life.
To overcome these restrictions, various arrangements of closed loop cooling systems were proposed in the art.
The term closed loop system, as used in this art, is not the same as hermetically sealed systems. In the disk file art, a closed loop system implies some provision to allow for makeup air since the enclosure is not hermetically sealed. Generally in such systems, the percent of makeup air required relative to the volume of air in the closed system is well below 5%, and generally below 1%. These closed loop cooling systems do avoid the filter life problem which resulted from pumping a huge volume of air through a filter. However, their applications have been limited to relatively small disk files or HDA's where the amount of heat generated within the enclosure is small and manageable and which can be dissipated through the walls of the HDA enclosure. Where closed loop cooling systems are used in large files, separate, expensive, heat exchangers for removing heat from the circulated air are required since the heat generated cannot be otherwise dissipated.
In early prior art disk file systems, the air bearing magnetic transducer never comes in contact with the surface of the disk. In these early files, the transducer positioning systems were designed to either retract the transducers by moving them radially out of the cylinder of the disks or by vertically unloading the head when the disks were not being rotated. In these arrangements, the possibility of generating debris internally of the enclosure from the disk surface was, therefore, relatively small. However, in an effort to improve the operation of the positioning system by reducing its mass, the start-stop in contact system was developed in which the heads are moved to an area of the disk referred to as the "landing zone" where no data was recorded prior to powering down the file. The start-stop in contact arrangement is one aspect of the "Winchester" type technology that is used extensively in disk files today. The fact that the transducer now contacts the moving disk surface during startup and power down operations increased the possibility of internal debris being generated which will be circulated by the closed loop system and may eventually cause a head crash.
Recently, the art has developed closed loop systems which employ start-stop in contact arrangements where a filter is provided in the closed loop path to filter part of the air. However, such systems are limited to file arrangements which have small disks or only one or two large disks because the heat dissipation capability of the closed loop system is diminished by inclusion of the filter for the same reasons that occurred in the prior art open loop type systems.
The present invention is directed to an improved closed loop cooling and filtering arrangement for a start-stop in contact type disk file which is capable of dissipating considerably more heat, thereby permitting an increase in storage capacity since an increase in the storage surface, i.e., more or larger disks, may be provided.